Idiopathic CD4+ T-lymphocytopenia (ICL) is a newly described immunodeficiency syndrome in which human immunodeficiency virus (HIV), the causative agent of acquired immune deficiency syndrome (AIDS), can not be detected (Laurence et al., 1992, Lancet 340: 273-74; CDC 1992, MMWR 41: 541-45; CDC 1992, MMWR 41: 578-79; Duncan et al., 1993, NEJM 328: 393-98; Ho et al., 1993, NEJM 328: 373-79; Spira et al., 1993, NEJM 328: 386-92). A definition of ICL by the Centers for Disease Prevention and Control (CDC) includes the repeated measurement of fewer than 300 CD4 cells/.mu.l in peripheral blood and repeated lack of seropositivity for human immunodeficiency virus (HIV), types I or II, or human T-lymphotropic virus (HTLV), types I or II. While some ICL patients belong to some of the same risk groups, such as male homosexuals, transfusion recipients, and intravenous drug abusers in which AIDS was first detected, a majority of patients do not belong to any risk group for HIV. As in AIDS, ICL patients have reduced numbers of CD4+ T-lymphocytes and many have developed the opportunistic infections or otherwise rare cancers associated with AIDS. Some ICL patients have died as a result of their immunodeficiency.
Although some aspects of this immunodeficiency resemble AIDS, HIV can not be detected in ICL patients. Confirmed ICL patients have proven to be negative for DNA sequences of HIV and HTLV by polymerase chain reaction (PCR) (Ho et al., supra; spira et al., supra). The causes of ICL are not known, and except for repeated CD4 quantitations there are no known methods for diagnosis of ICL.
In previous studies of autoimmune diseases, a human intracisternal A-type retroviral particle (HIAP-I) was identified in patients with Sjogren's Syndrome (SS), a systemic autoimmune disease (U.S. patent application Ser. No. 07/526,349 filed May 21, 1990 (Garry I); and also Garry et al., 1990, Science 250: 1127-29 (Garry II)). Another group recently described an intracisternal retroviral particle, designated "human intracisternal retroviral particle" (HICRV), in lymphoblastoid cells co-cultured with peripheral blood mononuclear cells from a 66-year old female patient with a history of Pneumocystis carinii pneumonia (PcP) (Gupta et al., 1992, PNAS 89: 7831-35). HICRV appears similar to HIAP-I, and is likely to represent a second isolation of that retrovirus.